This invention relates to a fuel controller for an internal combustion engine which measures the rate of air intake into the engine using an air flow sensor and controls the supply of fuel to the engine based on the output of the air flow sensor. More particularly, it relates to a fuel controller which employs a Karman vortex air flow sensor.
In an internal combustion engine which employs a fuel injection system, it is conventional to dispose an air flow sensor (hereinunder abbreviated as AFS) in an air intake pipe upstream of the throttle valve of the engine and to calculate the rate of air intake per each engine revolution based on the output of the AFS. The supply of fuel to fuel injectors for the engine is then controlled based on the calculated air intake rate.
Since the AFS is disposed upstream of the throttle valve, the air flow rate measured by the AFS does not always coincide with the actual air flow rate into the engine cylinders. In particular, when the throttle valve is abruptly opened, there is a sudden increase in the air flow through the AFS, but due to the provision of a surge tank between the throttle valve and the engine cylinders, the increase in the air flow rate into the cylinders is more gradual and of a smaller magnitude than that into the AFS. Accordingly, the air flow rate measured by the AFS is greater than the actual air flow rate into the engine, and if the fuel supply were controlled based solely on the value measured by the AFS during a single brief period when the air flow rate was in transition, the air-fuel mixture would be overly rich.
Therefore, the actual air flow rate into the engine cylinders is calculated as a weighted average of the value measured by the AFS over several periods, such as during two consecutive half-revolutions of the engine, and more accurate fuel control can be performed.
In many engines, blow-by gas which leaks from the cylinders into the crank case through gaps between the pistons and the cylinders is recirculated through a gas recovery passageway back to a portion of the air intake pipe between the AFS and the throttle valve and is once again sucked into the engine.
The AFS is commonly of the Karman vortex type. When the engine is running at a low speed, such as during idling, the Karman vortices which are generated by the AFS are not very strong. In this case, the blow-by gas which is introduced into the air intake pipe can significantly disturb the vortices and make them impossible for the AFS to measure. As a result, the amount of fuel which is supplied to the engine, which is calculated on the basis of the output of the AFS, will be inaccurate and the air-fuel ratio will greatly vary. This results in problems such as rough idling.